Lost Pictures - Kodak Z7590 Digital Camera

On several multi-week long road trips, I lost pictures in the middle of from 100+ to 250+ pictures taken on my Kodak Z7590 digital camera (has flash, zoom) using a SanDisk Standard SD 512MB memory card in the first case and the SanDisk Standard SD 2GB memory card in the 2nd case. These pictures are just not there. According to the camera, the 2GB card is capable of storing over 450 pictures. On both trips, I recharged the camera battery at least once. I do not recall any low battery warnings.

After a test photo working with their tech support, Kodak says that it is not the camera and told me to contact the memory card manufacturer.

Can anybody provide some explanation for this picture loss. Does the SanDisk card need more battery than the camera feels is needed?